Erythritol, a naturally occurring polyol sweetener, can be used to replace sugar while preserving the sweet taste. Erythritol is a four-carbon sugar polyol (tetritol), which possesses several properties such as sweetness (about 60-80% of sucrose), tooth friendliness, very low calorific value (0.2 kcal/g, 5% that of sucrose), non-carcinogenicity and, unlike other polyols, causes little, if any, gastro-intestinal discomfort (Harald and Bruxelles (1993) Starch/Starke 45:400-405). Further, erythritol possesses desirable processing properties such as heat-stability, and minimal undesirable reactivity with amino groups so as to resist browning of when present in an organic substance. Erythritol can be used as a sweetener, for example in beverages. For example, U.S. Pat. Nos. 4,902,525 and 6,066,345, JPA 7-274829 and EP 0 759 273 relate to the addition of erythritol to beverages for purposes of flavor enhancement. A chewing gum made with a sweetening agent containing erythritol and a liquid sugar or sugar alcohol is disclosed in U.S. Pat. No. 5,120,550. A method of reducing dental cavities by administering a sugarless chewing gum made with erythritol is disclosed in European Patent Publication No. 0 009 325. Low-caloric sweetening compositions containing mesoerythritol are disclosed in U.S. Pat. No. 5,080,916 and No. 4,902,525 and Japanese Patent Publications No. 89-225458 and 90-104259. Japanese Patent Publication No. 89-51045 discloses chewing gum made with a melted mixture of mesoerythritol and sugars or sugar alcohols. A sweetener employing the use of spray dried erythritol is disclosed in European Patent Publication No. 0 497 439. A sweetening composition made up of erythritol, sorbitol and a glucose oligomer is disclosed in European Patent Publication No. 0 511 761.
Erythritol can be found in lichens, hemp leaves, and mushrooms. Erythritol may also be found in fermented foods such as wine, soya sauce, or saki (Sasaki, T. (1989) Production technology of erythritol. Nippon Nogeikagaku Kaishi 63: 1130-1132). Industrial erythritol production is typically carried out by one of two approaches: chemical synthesis or fermentative biosynthesis.
Chemical synthesis of erythritol typically includes the addition of catalysts such as hydrogen and nickel to the raw material sugars under the environment of high temperature and high pressure. Decarboxylation reactions can be performed with hydrogen peroxide or hypochlorite, for instance. A suitable method is the so-called Ruff reaction, utilizing a combination of hydrogen peroxide and ferrous sulphate as a catalytic agent (see e.g. Ruff, Berichte der Deutschen Chemischen Gesellschaft 32 (1899) 553-554, and E. Fischer, O. Ruff, Ber. 33 (1900) 2142). Reduction can be carried out chemically, for instance by catalytic hydrogenation, or enzymatically. For example, calcium D-arabinonate may be in the presence of aqueous hydrogen peroxide solution. Other processes for the manufacture of D-erythrose include the oxidation of D-glucose in the presence of lead tetraacetate, known under the name of the Perlin method (Perlin A. S., Methods Carbohydr. Chem., 1962, 1, 64), or the acid hydrolysis of 2,4-O-ethylidene-D-erythrose obtained by the oxidation with periodate of 4,6-O-ethylidene-D-glucose (Schaffer R., J. Am. Chem. Soc., 81 (1959), 2838; Barker R. and MacDonald D. L., J. A. Chem. Soc., 82 (1960), 2301). A few improvements in the conversion of gluconic acid to D-arabinose have subsequently been introduced by R. C. Hockett and C. S. Hudson (J. Amer. Chem. Soc., 56, 1632-1633, (1934) and ibid., 72, 4546, (1950)) and by the document U.S. Pat. No. 3,755,294. Arabinose yields of 60%, starting from gluconic acid, are described therein. Progress has been accomplished by V. Bilik (CZ-232647, (1983)) by using cupric (Cu(II)) ions as catalysts. Yields of the order of 70% are achieved after a laborious purification. Identical results were recently obtained with a mixture of ferric and ferrous ions as catalysts (CZ-279002, (1994)). Finally, under specific conditions, the document EP-A 0,716,067 reports yields of certain aldoses of 78%. Another process is performed by the chemo-reduction of raw materials such as meso-tartarate (Kent, P. W., and Wood, K. R. (1964) J. Chem. Soc. 2493-2497) or erythrose (Otey, F. H., and Sloan, J. W. (1961) Ind. Eng. Chem. 53:267) to obtain erythritol. None of the known chemical synthesis techniques, such as reduction of meso-tartrate, oxidation/reduction of 4,6-O-ethylidene-D-glucose and hydrogenation of starch dialdehyde hydrolysates (T. Dola and T. Sasaki, Bio-Industry, (1988), 5, (9), 32), has been widely used for widespread industrial production. Still other chemical processes developed for the production of erythritol include the hydrogenation of tartaric acid to yield mixtures of tetritols, including erythritol (U.S. Pat. No. 5,756,865). Tartaric acid esters have also been reduced to yield erythritol (U.S. Pat. No. 2,571,967).
In addition, erythritol can be produced by a number of microorganisms. For example, the erythritol can be produced by fermenting glucose with specialized yeast strains has been described U.S. Pat. No. 5,902,739. Recovery of erythritol from fermentation broths is described in U.S. Pat. No. 6,030,820, U.S. Pat. No. 6,440,712 and U.S. Pat. No. 4,906,569. Microorganisms useful in the production of erythritol include high osmophilic yeasts, e.g., Pichia, Candida, Torulopsis, Trigonopsis, Moniliella, Aureobasidium, and Trichosporon sp. (Onishi, H. (1967) Hakko Kyokaish 25:495-506; Hajny et al. (1964) Appl. Microbiol. 12:240-246; Hattor, K., and Suziki, T. (1974) Agric. Biol. Chem. 38:1203-1208; Ishizuka, H., et al. (1989) J. Ferment. Bioeng. 68:310-314.) Production of erythritol by various yeasts have been reported: Debaryomyces (U.S. Pat. No. 2,986,495), Pichia (U.S. Pat. No. 2,986,495), Candida (U.S. Pat. No. 3,756,917), Moniliella (Antonie van Leeuwenhoek, 37 (1971), 107-118), and Aureobasidium (JP-A 61/31,091). Two microorganisms, namely, Moniliella tomentosa var. pollinis CBS461.67 and Aureobasidium sp. SN-G42 FERM P-8940, are known currently to be employed practically to produce erythritol. The former is employed, for example, in methods for producing polyols in an industrial scale by means of fermentation of saccharides (Japanese Patent Publication No. 6-30591 (30591/1994), ibid. 6-30592 (30592/1994), ibid. 6-30593 (30593/1994), ibid. 6-30594 (30594/1994)), and in these publications methods for producing a series of polyols including erythritol are disclosed. However, the strain of Moniliella tomentosa var. pollinis employed in such methods has a poor saccharide resistance and suffers from reduced yield of erythritol at a high saccharide concentration. Thus, at the saccharide concentration of 25 w/v % the saccharide-based erythritol yield (amount of erythritol produced relative to the amount of saccharide consumed) is as high as 42%, but at the saccharide concentration as high as 35 w/v % the saccharide-based erythritol yield is 33%, and at 35 w/v % the yield is as markedly low as 27%. Often, studies carried out on fermentation techniques produce erythritol as a secondary constituent. Possible disadvantages in the production of erythritol by fermentation include foaming during fermentation, an undesirably slow rate of fermentation, the amount of the byproducts and poor yield.
One of the major drawbacks of the use of erythritol as a sugar replacer is that it is much more expensive than some of the substances which it replaces. There is a need for improved, cost-effective processes for the manufacture of erythritol, or D-erythrose (converted to erythritol by hydrogenation of the D-erythrose thus obtained).